The present invention relates to an improved system and method for detecting the presence of a data-storage cartridge that is compatible with a particular type of disk drive. More particularly, the invention relates to a system and a method that utilize phase-rotated polarized light to detect the presence of a compatible data-storage cartridge.
Removable data-storage cartridges are commonly used to store digital information. Removable data-storage cartridges are utilized in conjunction with some type of disk drive that writes and reads the digital information to and from one or more recording surfaces on the medium. Removable data-storage cartridges can easily be inserted into and removed from the disk drive by the drive""s user, thereby allowing the drive to be utilized with different individual cartridges on a routine basis.
Data-storage cartridges typically comprise an outer casing, or shell, that houses a rotatable recording medium, or disk, upon which digital information is stored. The shell commonly includes upper and lower halves that are joined together to house the disk. The disk is mounted on a hub that rotates freely within the shell. The hub is adapted to engage a spindle motor of a disk drive when the cartridge is inserted into the drive. Activation of the spindle motor rotates the disk via the hub.
A disk drive typically writes or reads data to and from the disk""s recording surface through the use of one or more data-transducing heads. The outer shell of the cartridge usually has some form of opening near its forward edge to provide the heads with access to the recording surface. Some type of shutter or door mechanism is often provided to cover the access opening when the cartridge is not in use, thereby preventing dust and other contaminants from entering the cartridge and settling on the recording surface of the disk. (A particular type of data-storage cartridge has been described herein for exemplary purposes only; the term xe2x80x9cdata-storage cartridge,xe2x80x9d as used throughout the specification and claims, is intended to encompass all types of data storage devices, including tape cartridges.)
Disk drives typically comprise an actuator that positions the data-transducing heads proximate the recording medium. The actuator should not be permitted to translate unless a data-storage cartridge that is compatible with the disk drive is installed in the-drive. In particular, translation of the actuator should not be permitted unless a data-storage cartridge having an appropriate form factor, i.e., outer dimensions and geometry, is present in the drive. Movement of the actuator in the presence of a foreign object can damage the actuator and the data-transducing heads. (The term xe2x80x9cforeign object,xe2x80x9d as used throughout the specification, refers to data-storage cartridges having a form factor that is incompatible with a particular drive, and objects other than data-storage cartridges.) Furthermore, movement of the actuator in the presence of an incompatible data-storage cartridge can corrupt the data that is stored on the cartridge.
Most removable-media drives utilize data-storage cartridges having similar form factors. Additionally, many types of foreign objects other than incompatible data-storage cartridges are easily inserted into disk drives. Thus, removable-media disk drives commonly require some type of mechanism for detecting the presence of a compatible data-storage cartridge within the drive. In particular, the mechanism should be able to discriminate between compatible data-storage cartridges and foreign objects.
Removable-media disk drives commonly include mechanical switches that detect the presence of a data-storage cartridge within the drive. These switches are typically positioned so that the complete insertion of a data-storage cartridge into the drive causes the cartridge to contact the switch, thereby producing an indication that a cartridge is present within the drive.
Cartridge-detection systems that use reflective materials have been developed and patented. For example, U.S. Pat. No. 5,638,228 (xe2x80x9cthe ""228 patentxe2x80x9d) describes one such system. The ""228 patent issued on Jun. 10, 1997, and is incorporated herein by reference in its entirety. The ""228 patent describes a data-storage cartridge comprising a marker formed from a retro-reflective material. The retro-reflective marker is disposed on an outer shell of the cartridge. The ""228 patent also discloses a disk drive that employs a light emitter and a light detector coupled to an electrical circuit. These components determine whether a compatible data-storage cartridge is present in the drive by sensing the presence of the retro-reflective marker.
The light emitter described in the ""228 patent directs radiant energy, i.e., light, at the retro-reflective marker. A portion of the light that is incident upon the marker is reflected back toward the light source, i.e., the emitter. The detector is positioned proximate the emitter, and senses the intensity of the reflected light.
The amount of incident light reflected by a retro-reflective marker is greater than the amount of light reflected by most other objects under similar conditions. The retro-reflective marker thus generates a relatively strong reflection when illuminated by light from the emitter. Hence, by sensing that an amount of light reflected from an object inserted into the disk drive exceeds a predetermined threshold, the detector and the electrical circuit can generally recognize the presence of a data-storage cartridge equipped with a retro-reflective marker.
The electrical circuit permits movement of the drive""s actuator when the amount of light incident upon the detector exceeds the predetermined threshold. The electrical circuit thereby allows the data-transducing heads to interface with the data-storage cartridge. Conversely, amounts of reflected light that do not reach the predetermined threshold are interpreted by the electrical circuit as an indication that a compatible data cartridge is not present in the drive. Hence, the electrical circuit does not permit movement of the actuator under such circumstances.
The system described in the ""228 patent has proven to be effective in detecting the presence of compatible data-storage cartridges within disk drives. Under certain limited circumstances, however, the ""228 system permits activation of the drive""s actuator in the presence of specific types of foreign objects. Activation occurs under these circumstances because a relatively limited number of materials have surface reflectivities similar to or greater than that of the retro-reflective marker. Hence, objects formed from these materials, when inserted into a disk drive equipped with the ""228 system, are recognized by the drive as a compatible data-storage cartridge.
As is evident from the above discussion, a need exists for a cartridge-detection system that provides a greater degree of differentiation between compatible data-storage cartridges and certain types of foreign objects. The present invention is directed to this and other goals.
An object of the present invention is to provide a disk drive having an improved ability to discriminate between compatible data-storage cartridges and foreign objects within the disk drive. In accordance with this object, a presently-preferred embodiment of the invention comprises a disk drive that includes a source of polarized light and a detector being in selective optical communication with the source of polarized light. The detector detects polarized light having predetermined characteristics. The detector preferably comprises a polarizing filter. The polarizing filter is in selective optical communication with the source of polarized light.
In one particular embodiment of the invention, the source of polarized light emits polarized light having first polarization angle, and the detector is adapted to respond maximally to polarized light having a second polarization angle. In a further embodiment, the disk drive is adapted to receive a data-storage cartridge having a retro-reflective marker. The retro-reflective marker places the source of polarized light and the detector in optical communication when the disk drive receives the data-storage cartridge. The retro-reflective marker rotates the polarization angle of the polarized light emitted by the source of polarized light from the first polarization angle to approximately the second polarization angle.
Further in accordance with the above-noted object, the invention provides a data-storage system comprising a disk drive that includes a source of polarized light and a light detector. The data-storage system also comprises a data-storage cartridge adapted for insertion into the disk drive. The data-storage cartridge comprises a reflective marker that forms an optical path between the source of polarized light and the light detector when the data-storage cartridge is inserted into the disk drive.
In one particular embodiment of the invention, the source of polarized light emits polarized light having a first polarization angle and the light detector is adapted to respond maximally to polarized light having a second polarization angle. The reflective marker preferably rotates a polarization angle of the light emitted by the source of polarized light from the first polarization angle to approximately the second polarization angle.
Another object of the present invention is to provide an improved method for discriminating between compatible data-storage cartridges and foreign objects within a disk drive. In accordance with this object, a method for detecting the presence of a data-storage cartridge in a disk drive comprises the step of directing polarized light at a reflective marker disposed on the data-storage cartridge. The method further comprises the steps of measuring an amount of the polarized light that is reflected by the marker, and determining whether the amount of reflected light exceeds a predetermined threshold.